Present day processing technology enables the fabrication of magnetic heads at a miniaturized scale. To achieve this end, circuit components are scaled down both in areal dimension and in height dimension with thinner interposing layers. However, there are certain thickness limits the interposing layers need to maintain. Beyond such limits, various reliability problems may arise. For example, in a magnetic head, the read-write gap is formed of an insulating layer spacing two magnetic layers. A thinner gap offers the benefit of allowing the magnetic head to process high density data signals. However, the thinner insulating layer forming the gap is more prone to pinholes, which may bridge the magnetic layers and render the magnetic head inoperable. For example, where an insulating layer separates two conducting layers, a thin insulating layer may be incapable of withstanding the electric fields emanating from the two conducting layers. Consequently, the insulating layer may experience a dielectric breakdown, which results in a disastrous failure. Accordingly, there is a need to provide high quality insulating films to meet the demands of the magnetic recording head industry.
Materials most commonly used as insulating layers in magnetic recording heads are alumina (Al.sub.2 O.sub.3) and silicon dioxide (SiO.sub.2). The quality of these insulating layers can be gauged by a number of parameters. A good insulating film is uniform in thickness over a large surface area, thereby allowing the overlying layers to assume good step coverage. In addition, the film should be free of pinholes, thereby preventing any magnetic or electrical shorts of the overlying and underlying layers. Furthermore, a good insulating film is capable of withstanding high electric breakdown voltage, and is resistant to certain chemical etchants.
Insulating films can either be thermally grown by oxidation or by deposition. For instance, SiO.sub.2 can be grown out of a silicon substrate via the process of oxidation. However, when the substrate material is different from the insulating material, deposition methods are preferred. U.S. Pat. No. 5,256,266 to Blanchette et al. discloses a process for sputtering and depositing alumina that is crypto-crystalline and is useful as the insulating layer which forms the transducing gap of the head.
Thin film deposition may be accomplished by sputtering, chemical vapor deposition (CVD) or plasma enhanced CVE) (PECVD). One example of depositing insulating thin films by sputtering is described herein with reference to FIG. 1. A typical arrangement for depositing insulating thin films during magnetic head fabrication employs a sputterer 2 encased within a chamber 4. Fixed inside the chamber 4 are a target plate 6 and a substrate fixture 8. Secured atop the substrate fixture 8 are substrates 10 of the magnetic recording heads to be processed. The target plate 6 is normally formed of material to be deposited onto the substrate 10. For example, as shown in FIG. 1, the target plate 6 is made of alumina.
Prior to the deposition process, air is first pumped out of the chamber 4 in a direction signified by arrow 12 via outlet 14. After a satisfactory vacuum level inside chamber 4 is reached, an inert gas, such as argon (Ar), is then admitted into the chamber 4 in a direction designated by arrow 16 via an inlet 18. When the inert gas inside the chamber 4 reaches a sufficiently high pressure level, the sputterer 2 is then ready for operation.
The target 6 and the substrate fixture 8 are normally biased through a steep electric potential by the voltage source 20 in the range of 500 Volts to 1000 Volts. The inert gas atoms between the target 6 and the substrate fixture 8 are thereby ionized. In essence, the electrons of the inert gas atoms are attracted toward the substrate fixture 8 while the positively charged ions 22 move toward the target 6. In the process, target molecules 24 are dislodged and dispersed from the target 6 and deposited onto the substrate 10 as the insulating thin film. It should be noted that the above description is depicted at the molecular level. Actually, the gas ions 22 form a plasma 26 bombarding the target 6 constantly.
The sputtering method, as described above, has been widely used in the processing of electronic circuits. However, there are several drawbacks associated with this method. First, inert gas inside the chamber 4 must be at a relatively high pressure in order to sustain a plasma. Very often, at such high pressure level, impurities inside the inert gas can easily be deposited onto the substrate surfaces, resulting in deposited films with high pinhole counts. Equally as undesirable, both the target plate 6 and the substrate fixture 8 of the sputtering apparatus 2 are tied to high voltage potentials. The target plate 6 especially and the substrate fixture 8 are practically incapable of any mechanical motions. The main reason is that any relative motions between the target plate 6 and the substrate fixture 8 would disturb the sustained plasma 26 and negatively affect the sputtering process. However, with the substrate 10 stationary relative to the target 6, the target molecules 24 may not be uniformly deposited onto the surfaces of the substrate 10. Consequently, the insulating films may be deposited with uneven thickness.
For electronic circuits having large geometrical sizes, insulating thin films fabricated from the sputtering method may be capable of fulfilling their intended functions. However, as circuits scale down in physical dimensions, conventionally deposited insulating films with the aforementioned shortfalls could affect the final production yield and reliability.